High strength bolts torque values

[ASFI]

I am sorry I had to post this here, but I didnt get much replies in the fastening section, I hope you can help:

In Australia, to follow the standards AS3990 and AS4100, what should be the torque values for HSS bolts (grade 8.8) using a torque wrench?
For example I think it should be 580Nm for M20 galvanised bolts .However everybody seems to use 370Nm
I have calculated as follows for M20:
1- T = K x Fi x D
2- Fi = 87 / 0.6 = 145 Kn. Minimum bolt pretension as per appendix F in AS3990. This is to drive the bolt to proof stress as i can see
3- K = 0.2 for galavanised
4- D = 20
Therefrore T=580 Nm.
this way all the threads are engaged and the bolt can actually surpass its yield strength and not be subjected much for fatigue, this is why the code prohibits using already torqued bolts.

Thank you all

 

[MikeHalloran]

Correction:

You didn't get the answer you wanted in the fastening section.

You in fact got two answers that both boil down to "You're doing it wrong."


The forum that tells you what you want to hear is elsewhere.





Mike Halloran
Pembroke Pines, FL, USA

 

[apsix]

Using a torque wrench is not a recognised method of tensioning structural bolts (in Oz) - too many variables.

 

[msquared48]

Oh...Sorry. I mistook the subject as torqued wenches.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[apsix]

It's best not to stalk anyone, including wenches.

 

[cap4000]

Your formula is used in the ASCE book Wind Loads for Anchor Bolts for Petrochemical Facilities. However, the AISC manual does not recognize using a torque wrench because it can be as much as 40% off. The K value is critical. The Bolt Council allows a torque wrench under its arbritration clause but you first must have 3 bolts tested in a lab.

 

[rscassar]

I know you didn't specifically address this but this is what I request:

Method of tensioning: Grade 8.8TF or TB bolts shall be tensioned using a "coronet" load indicating washer or the part turn method (see AS 4100 15.2.5). Torque wrenches shall not be used for final tensioning.

 

[ASFI]

Thank you all for your replies.

I am familiar with the torque of the nut procedure to torque HSS bolts and I know the torque wrench is not a good method.

However, some people have been using this method (torque wrench) for a long time and it is a bit hard to convince otherwise.

I will try again

 

[a2mfk]

Just on your last comment- if we never moved ahead technologically when a better way of doing things came along, we would certainly not be on this message board!! Just educate yourself enough to educate others, and point them to specific articles/codes to back yourself up. This usually works...